overheat monitor with auto poweroff

- needs passwordless sudo on target machine or deploy to run as root

pi/ui/lib/app_root.dart

@@ -2,6 +2,9 @@ import 'package:flutter/material.dart';
 
 import 'screens/splash_screen.dart';
 import 'screens/dashboard_screen.dart';
+import 'screens/overheat_screen.dart';
+import 'services/config_service.dart';
+import 'services/overheat_monitor.dart';
 
 /// Root widget that manages app state transitions
 class AppRoot extends StatefulWidget {
@@ -13,6 +16,7 @@ class AppRoot extends StatefulWidget {
 
 class _AppRootState extends State<AppRoot> {
   bool _initialized = false;
+  bool _overheatTriggered = false;
   String _initStatus = 'Starting...';
 
   @override
@@ -21,7 +25,17 @@ class _AppRootState extends State<AppRoot> {
     _runInitSequence();
   }
 
+  @override
+  void dispose() {
+    OverheatMonitor.instance.stop();
+    super.dispose();
+  }
+
   Future<void> _runInitSequence() async {
+    // Load config first
+    setState(() => _initStatus = 'Loading config...');
+    await ConfigService.instance.load();
+
     // Simulate init checks - replace with real checks later
     // (UART, GPS, sensors, etc.)
 
@@ -37,16 +51,31 @@ class _AppRootState extends State<AppRoot> {
     setState(() => _initStatus = 'Ready');
     await Future.delayed(const Duration(milliseconds: 300));
 
+    // Start overheat monitoring
+    OverheatMonitor.instance.start(
+      onOverheat: () {
+        setState(() => _overheatTriggered = true);
+      },
+    );
+
     setState(() => _initialized = true);
   }
 
   @override
   Widget build(BuildContext context) {
+    // Determine which screen to show (priority: overheat > splash > dashboard)
+    Widget child;
+    if (_overheatTriggered) {
+      child = const OverheatScreen(key: ValueKey('overheat'));
+    } else if (!_initialized) {
+      child = SplashScreen(key: const ValueKey('splash'), status: _initStatus);
+    } else {
+      child = const DashboardScreen(key: ValueKey('dashboard'));
+    }
+
     return AnimatedSwitcher(
       duration: const Duration(milliseconds: 500),
-      child: _initialized
-          ? const DashboardScreen(key: ValueKey('dashboard'))
-          : SplashScreen(key: const ValueKey('splash'), status: _initStatus),
+      child: child,
     );
   }
 }